1. Field of the Invention
The present invention relates to an improved drywall edge finishing structure for use in covering edges and corners of interior building walls constructed of wallboard panels.
2. Description of the Prior Art
In current building construction techniques, sheets of drywall, sometimes called wallboard, are widely used to form the surfaces of interior walls of residential, commercial and industrial buildings. Drywall has widely replaced plaster as the standard interior building wall fabrication material due to the speed and ease with which it can be installed. Drywall, or wallboard, is formed of sheets of plaster which are sheathed in an outer wrapping of heavy construction paper. Large sheets of drywall are typically provided at the construction site in sizes of four feet by eight feet or four feet by twelve feet. The drywall sheets are sometimes installed intact, but it is usually necessary to cut them to size to form interior building walls.
Drywall tape is widely used in the building construction industry as a means for covering the crevices between abutting panels of drywall. Conventional drywall tape is provided in narrow, elongated ribbons or strips of porous paper wound into rolls. The paper is sometimes perforated in increase moisture penetration and to prevent air bubbles from being entrapped behind the tape. The drywall tape is first applied to joints and edges of abutting drywall panels and is then covered with wet plaster, sometimes called "mud". The plaster is feathered and smoothed along the edges of the tape to conceal the demarcations between the tape edges and the drywall panels to which the tape is applied. Once the wet plaster has dried the tape and the drywall can be pained or otherwise covered with a suitable wall covering. Because drywall tape is formed of paper it is quite flexible and will conform to various surface configurations of the edges of intersecting panels of drywall.
While the edges, as well as the flat, expansive surfaces of sheets of drywall are originally covered with heavy paper, the edges of encapsulated sheets of plaster therewithin are exposed where the sheets of drywall are cut to size. When the severed edges of the drywall sheets are exposed, the exposed plaster does tend to crumble unless the severed edges are somehow protected. This is especially important at exterior wall edges where wall surfaces meet within the interior of a building. Such exterior edges define doorways and window openings, in contradistinction to interior edges, such as those formed by intersecting drywall panels in the corner of a room, for example. That is, exterior edges are those edges in which the building walls encompass an angle of less than 180 degrees, while in an interior edge the building walls encompass a reflex angle.
When conventional drywall tape is used at the exterior edges of walls, however, the flexibility of the tape often results in a corner demarcation which is irregular, since the tape does conform to irregularities in the exposed, severed edges of the drywall panels. As a consequence, conventional drywall tape is often not used at exposed exterior corners.
To finish exterior edges in building construction, metal corner beads are often employed. Conventional metal beads are configured in an L-shaped or angle-shaped cross section and are typically fabricated from elongated perforated strips of metal, such as galvanized steel, permanently deformed with a lengthwise 90 degree bend to form elongated angles. The metal beading is typically positioned at the intersections of adjacent drywall panels which meet at right angles to form an exterior edge within a room. The sections of metal beading are nailed in place through the drywall panels to wooden supporting structural members located behind the drywall panels. Wet plaster is then smoothed into place to cover the metal bead or leg members of the metal beading, and the edges of the plaster are smoothed and feathered to attempt to conceal the metal edges.
While the rigidity of the metal beading does allow an exterior corner of an interior building wall to be finished with a sharp, straight edge which is aesthetically pleasing, the use of metal beading involves several significant problems. Specifically, since the adjacent angle flanges of the metal beading are rigid so as to preserve the straight, linear configuration of the apex of the beading, the metal beading will only conform to straight, linear edges formed by orthogonal sections of drywall panels. The metal beading will not conform to drywall edges which are cut in an arcuate shape to form, for example, an arched doorway.
Also, the flanges of the metal beading are significantly stiffer than paper drywall tape, and do not always readily lay flat against the surfaces of the drywall. Consequently, the flanges of the metal beading can be concealed only with the application of a considerably greater amount of wet plaster, as compared with the amount of wet plaster required to conceal conventional drywall tape. This results in both an increased material cost as well as a substantially increased labor cost. Moreover, at locations where the flanges of the metal corner beads do not reside in intimate contact with the drywall surface, the dried plaster between the flanges of the metal bead and the drywall will tend to crumble, particularly if any pressure is exerted on the flanges cf the metal corner bead. Furthermore, over a period of time the metal corner bead will rust, thereby producing rust stains which are clearly visible on the surfaces of the walls at the edges thereof.
A further disadvantage of conventional drywall edge finishing systems is that the edge finishing structures, such as metal beading, must be held in position and nailed into place. Frequently nails which are pounded into the flanges of the metal beading do not strike solid structural supports behind the wallboard, but rather pass outside or between solid supports such as studs and joists. As a consequence, conventional beading is not always adequately anchored against the wall. Portions of the flanges of such metal beading will thereupon separate from the wallboard against which the beading is disposed, thereby creating cracks running parallel to the intersecting wall edges covered by the beading in the wall finish. Such cracks give an unsightly appearance to the finished wall surface of a room.